Method of making electromagnetic induction apparatus



.Mmga fi 'fl fla J. J. VIENNEAU METHOD OF MAKING ELECTROMAGNETICINDUCTION APPARATUS 2 Sheets-Emmi Original Filed may 24;, 1945h'fik/emtcj'r: Jacob J. Viewwneau,

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His Atnmwnev J. J VIENNEAU ETHOD OF MAKING ELECTROMAGNETIC INDUCTIONAPPARATUS migmal Filed Maya-4; 19%

2 Shasta-Swat 2 Inventor: Jacob J. Vienneau,

His Attorne Patented Aug. 2, 1949 METHOD OF MAKING ELECTROMAGNETICINDUCTION APPARATUS Jacob J. Vienneau, Pittsfield, Mass., assignor toGeneral Electric Company, a corporation New York Original applicationMay 24, 1945, Serial No. 595,518. Divided and this application June 17,1946, Serial No. 677,390

4 Claims.

This invention relates'to a method of making electromagnetic apparatusand more particularly to a method of making magnetic cores for suchapparatus.

This is a division of my application Serial No. 595,518, filed May 24,1945, and assigned to the present assignee.

Since the comparatively recent discovery of magnetic materials havingsubstantially lower losses than heretofore, when the flux is in aparticular direction therein, the problem has been how best to utilizesuch materials in magnetic cores. By best utilization is meant theoptimum relation .between economy in manufacture and reduction inlosses, and it is to be understood that these two considerations usuallyconflict.

One well-known way of using the directional properties of the newer coresteels is to form it in the shape of a flat strip or ribbon with thegrain or most favorable magnetic direction'coinciding with itslengthwise dimension and winding or bending it flatwise into amulti-layer closed magnetic loop. The flux then always goes with thegrain and low losses result. However, there is then the problem ofgetting the coil or conductive winding to link the closed core. Numerousways of overcoming this difficulty have been suggested and one is to outcompletely through the core so that the parts can be separated forreceiving a preformed coil. This in turn results in joints or gaps inthe magnetic circuit which increase the magnetizing current andsometimes increase the eddy current losses. Special treatment of the cutends has also been used to reduce such losses.

In practicing this invention the closed magnetic loop is cut at only oneplace, so as to have the minimum number ,of gaps or joints, and the endsare bent apart to permit the insertion of the coil and are then broughttogether again. This in itself is not new and it was suggested in 1889,long before the discovery of low loss directional steels, in BritishPatent 7,856 to Johnson and Phillips. However, the British constructionis not practical and is especially unsuitable when low loss directionalsteel is used. In the first place, it is practically impossible to bringthe edges of the out together again once the core has been bent openenough to allow the insertion of the coil. This is because the adjacentlayers of strip bind on each other. The result is that av gap is formedwith the closed point of the V at the inner peand the outer layers underheavy tension. In the second place, such stresses in directional steelwould greatly increase its hysteresis losses as it is well known thatthis material is very sensitive to stresses and strains. In the thirdplace, the adjacent layers at the cut edges would be under heavy radialpressure, thus greatly increasing the tendency for burrs produced by thecutting to short circuit the layers and increase the eddy currentlosses.

This invention is characterized by providing a predetermined spacebetween the turns or layers of such a core. As a result the gap can beadjusted or reclosed without difiiculty. Furthermore, this space causesthe gap initially to assume a V shape with the closed'part of the V atthe outer periphery of the core and specially located clamping means isprovided so that as the arms of the V are closed the outer layers of thecore are progressively separated in a radial direction, thus effectivelypreventing burrs at the butt Joints from short circuiting thelaminations.

An object of the invention is to provide a novel method of making amagnetic core for electromagnetic induction apparatus.

Another object of the invention is to provide a novel method ofinterlinking a conductive winding and a magnetic core.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawings and its scope will bepointed out in the appended claims.

In the drawings Fig. 1 is a side elevation View illustrating how thecore may be wound on a mandrel, Fig. 2 is an edge elevation of the coreshown in Fig. 1, Fig. 3 is a side elevation view illustrating a way of.fastening the turns or layers .of the core together and alsoillustrating a desirable location of the fastening means, Fig. 4 is anedge elevation of the core shown in Fig. 3 and illustrates further theposition of a clamping bracket which is preferably attached to the coreby the same means which fastens its turns or layers together, Fig. 5illustrates the step of annealing the core, Fig. 6 illustrates thelocation of a cut in the core, Fig. '7 illustrates the change in theshape of the cut or joint after the spacing strip or filler materialbetween the turns of magnetic strip has been removed so as to providepredetermined spaces between these turns, Fig. 8 shows how two of thecut loop cores are mounted relatively to each other and their cut endsspread apart so as to receive a coil winding on their common centerwinding leg, Fig. 9 shows the two core parts drawn together by aclamping screw of Fig. l1, Figs. 13 and 14 show a modified form of Aclamping bracket, Figs. 15 and in show another form of clamping bracket,and Fig. 17 shows the use of a key for strengthening the butt joint inthe core.

Referring now to the drawings and more particularly to Fig. 1, there isshown therein a mandrel i which is mounted for rotation about an axis(perpendicular to the drawing) in any suitable manner, such as in alathe (not shown) The mandrel may be or any suitable shape and, asshown, it is substantially rectangular but, as will be explained later,it is preferable to have it slightly trapezoidal. Wound on this mandrelare a magnetic strip or ribbon 2 and thinner spacing strip 3 which maybe made of paper. The strips are wound one on. top of the other so thatthe spacing strip is between the layers of the magnetic stri, Themagnetic strip is preferably of the type which has a most favorablemagnetic direction, that is to say, its hysteresis losses and re--luctance are lowest for flux in a given direction and this direction ialong the length of the strip.

The thickness of both the magnetic strip and. the spacing strip relativeto the over-all core thickness or number of turns or layers of the striphas been exaggerated for the purpose of showing more clearly theprincipal features of the invention and it should be understood that inpractice both strips will be very much thinner and will makecorrespondingly more turns or layers.

The stripsmay be of any suitable width so that, for example, the coremay have the relative dimensions shown in Fig. 2, which is an edge viewof the core.

After as many layers of magnetic strip have been wound on the mandrel asare necessary to give the desired flux density in the iron, the turnsare securely fastened together in any suitable manner. For example, theymay be welded together in a line along their edges as shown in Fig. 3where the weld is indicated at d. This same weld may also serve toattach a clamping bracket 5 to the core and, as shown in Fig. 4, thisbracket i bent over so that it terminates above the center of the core.After the turns have been securely fastened together the strips may becut off as at 6 in Fig. 3.

It is important that the weld 4 be on one side of the core only soas notto provide a. short circuit path for eddy currents, as such a path wouldsubstantially increase the eddy current losse in the core.

After the turns of the core have been securely fastened together, thecore is preferably annealed so as to free the magnetic material from allstrains thus reduce its losses to a minimum. As the core when it isassembled with its coil is normally sped together, it is preferable thatthe core be alder an equivalent pressure or compression when is i beingannealed so that its normal operating state will be as close as possibleto its state when it comes out of the annealing furnace. Therefore, itis preferable to place the distributed core.

core on its side with a weight i on top of it when it is in theannealing furnace.

After the core has been annealed the mandrel l is removed and the core icompletely out through as indicated at 8. This cut may be made by anysuitable means, preferred device being an abrasive wheel. The cut 8 isin a part of the yoke portion of the core which is in line with thewinding leg portions of the core. Thus, in Fig. 6, 9 indicates thewinding leg of the core and the out is made past the end of this leg inthat part of the yoke portion of the core which is in line with thewinding leg 3. Note that the weld d and bracket are on the yoke portionof the core relatively near the out 8.

If the mandrel l were exactly rectangular the core material removed bythe cut 2- would result in a slightly trapezoidal core when the out 3 isclosed to form a butt joint. This would give a poor space factor withrectangular coil. Therefore, in order to compensate for the width of cut8, the mandrel is preferably made slightly trapezoidal, the widest partbeing at the cor and which is to be cut.

The spacing means or spacing strip between the adjacent layers of themagnetic strip is now re moved from the core. When the spacer is paperstrip it will be turned to ash when the core is annealed and thereforeit can be blown out from between the metal layers by compressed air andthis will be facilitated by slightly flexing the core so as to separateslightly the adjacent layers of metal. After the spacing strip has beenremoved there will be a predetermined free space between each layer ofthe core with the result that the cut 8, instead of having parallelsides as in Fig. .6, will now be V-shaped. as in 7 with the point orclosed part of the V at the outer periphcry of the core This is becauseas the layers are considered from the innermost to the outermost they ineffect get progressively longer due to the removal of the spacing stripso that the outer layer will butt together first at the cut 8 and theneach succeeding inner layer being relatively shorter will have arelatively greater space between its out ends.

Another way to remove the spacer strip is to loosen carefully the coreturn by partially unwinding the core into an eight-sided figure and thenpull or shake the spacer strip out. The core is then rewound to theshape it had while it was being annealed.

The cut 8 can also be made before the core is annealed but its turnsshould first be fastened together as by the weld 4 so a to prevent itfrom coming apart after it had been cut.

The core indicated in Fig. 7 can now be spread apart at the cut 8 so asto slip a coil or winding on the winding leg 9. While a single core loopas shown in Fig. 7 can be used, it is usually preferable to use two ormore so as to provide a so-called Fig. 8 shows a two-part distributedcore withthe Winding legs 9 wrapped together with insulating materialI!) and with the parts spread apart at the cuts so as to provide spacefor slipping the coil i I in place. While only a two-part core has beenillustrated, it will be obvious to those skilled in the art that thedistributed core can have any desired additional number of parts.

After the coil II has been slid into place the yoke portions of the coreare bent back into place so as to close the gaps 8 and a clamping boltI2 is inserted in clamping brackets 5 and nuts I3 on the ends thereofare drawn up.

The w'rapping I 0, as shown most clearly in Fig. 8, binds the windinglegs relatively tightly together so as to provide a favorable spacefactor in the coil window and this results in separating the layers ofthe core at the corners indicated at M in Fig. 9. Alternatively, thecore may be inserted into the coil one leg at a time and then forcedtightly against the sides of the coil with a spacer l5. Fig. is anenlarged view of the right-hand core part in Fig. 9 showing how thelayers have little space between them in the winding leg 9 and haverelatively large spaces between them at the corner Hi. This makes itpossible for the yoke portion of the core to be bent very easily in thedirection of the arrow in Fig. 10 so as to close the gap 8 withoutexcessively straining the magnetic material.

As the nuts l3 on the clamping screw are drawn up the cut ends of theouter turn or layer of the core first come into abutting relation.Continued tightening of the nuts causes the outer layer of both sides ofthe cut to spring outward slightly .so that the cut ends of the nextlayer come into abutting relation. Continued tightening of the nutstherefore progressively causes the layers to come into abutting relationand then to spring outwardly slightly so that the next succeeding layerin the inwardly extending direction will come into abutting relation.This continues until the cut ends of all of the layers are in abuttingrelation. By reason of the separation between layers at the cut it willbe seen that it is difficult for adjacent layers to be short circuitedby minute burrs which are usually raised at the cut edges during thecutting operation. Consequently,

the butt joint does not need to have its surfaces smooth worked ortreated in any special way and no noticeable increase in eddy currentlosses is produced by my improved butt joint. Also, as the cut ends ofeach layer are in abutting relation the reluctance of the joint'is quitelow and hence the exciting ampere-turns of the core are relatively lowcompared with other butt-jointed cores.

In order to strengthen the joint and also to make additionally sure thatits laminations are insulated from each other the abutting faces of thejoint are preferably coated with an insulating varnish, such as a thermosetting synthetic resin, before they are clamped together. The

above-described spreading action of the joint laminations then allowsthe varnish to run between the laminations with the result that they arewell insulated and are firmly held in place after the varnish becomeshard.

It is not essential to my invention that the joint be in the yokeportion of the core and it can also be in the winding leg portion of thecore. Furthermore, the joint need not be closed and it can be kept openmagnetically any desired amount was to provide an air gap. An example ofsuch construction is shown in Fig. 11 and it is particularly welladapted for use with reactors. In this figure the gaps 8 are shown inthe winding legs 9, near one end thereof, and they are spaced bysuitable non-magnetic insulating spacers l6 which are inserted betweenthe cut ends of the winding legs.

The core parts are shown welded in two places and these welds also serveto fasten brackets H in place. These brackets bear against upper andlower clamp members l8 and [9 respectively which are pulled together byclamping poles 20. In order to prevent the brackets 18 and I9 fromslipping relative to the members l1 pins 2| passing through registeringholes in the members l1,

l8 and 19 are provided. V

The core parts are sufilciently flexible so that when the cuts or gaps 8are near the. ends of the winding legs the core parts can be broughttogether readily after the coil II has been put in place in the mannershown in Fig. 8. As the clamping bolts 20 are tightened the ends of thelaminations will be progressively pressed against the insulating spacersl6 so as to separate them slightly in a manner similar to the way the1aminations are spread apart, as shown in Fig. 9.

It is not essential to fasten the core turns together by welding nor isit essential that the clamping brackets be attached to the core bywelding and these brackets can be made of insulating material which iscemented to the core. Such construction is shown in Figs. 13 and 14,-inwhich one-piece brackets 22 of insulating material are U-shaped and fittightly over the yoke portions of the core and are cemented to the coreby any suitable adhesive cement, such as a polyvinyl butyral-phenolaldehyde resin solution. In addition, these brackets can be held inplace by bolts 23 which pass through the core. The space for permittingthese bolts to pass through the core is provided by placing a spacer inthe core at the necessary point when the core is being wound. After thecore is annealed this spacer is removed the same time that the spacingstrip between the magnetic strip is removed.

In the modified construction shown in Figs. 15 and 16 a two-partclamping bracket 24 is provided and the bolt 23 instead of passingthrough the core passes through the bracket 26 outside of the core. Thebracket 26 is preferably also cemented to the core as in Figs. 13 and14.

In order to strengthen the core joint one or more keys 25 may be placedbetween the cut laminations so as to straddle the joint, as shown inFig. 17. The space for the key is provided by inserting a metal spacerin the core when it is wound. The two halves of this spacer are removedafter the core has been cut at 8 so as to provide space for the key.

While there has been shown and described a particular embodiment of thisinvention, it will be obvious to those skilled in the art that variouschanges and modifications can be made therein without departing from theinvention and, therefore, it is aimed in the appended claims to coverall such changes and modifications as fall within the true spirit andscope'of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method of making a magnetic core for electromagnetic inductionapparatus which comprises, winding on a mandrel a steel strip with aspacing strip between turns of the steel strip so as to form a woundcore having a winding leg, a yoke leg and two end yokes, attaching aclamping bracket to said core by welding across all the turns of saidwound strip on one side of the core near the junction of the yoke legand one end yoke, annealing said core, removing the mandrel, cuttingcompletely through said core near the junction of said winding leg andwelded end yoke, removing said spacing strip to form a V-shaped jointwith the closed end of the V at the outer periphery of the core, andurging said clamping bracket toward said winding leg whereby the layersof steel strip adjacent the V joint are radially separated in order thatthe cut ends of the strip form butt joints at each layer.

2. The method of making a magnetic core for electromagnetic inductionapparatus which comprises. winding a steel strip and an organic spacingstrip in interleaved relation on a mandrel so as to provide a wound corehaving a winding leg and a yoke portion, securely fastening the turns ofsaid steel strip together in the yoke portion substantially nearer oneend of the winding leg than its other end, annealing the core, removingthe mandrel, completely cutting through the core substantially withinthe lateral confines of the winding leg and near said one end thereof,removing said spacing strip whereby after said core is spread apart atsaid out to allow insertion of said winding leg through a coil windowthe core can be closed again without excessively straining the layers ofsteel strip, and forcing the cut ends of the core together so as toprovide a butt joint at which adjacent layers of steel strip areradially separated so as to prevent short circuits between adjacentlayers by burrs raised during the cutting.

3. The method of making a magnetic core for an electromagnetic inductionapparatus which comprises, winding a steel strip and a spacing strip ininterleaved relation on a mandrel so as to provide a wound core having awinding leg and a yoke portion, securely fastening the turns of saidsteel strip together in the yoke portion substantially nearer one end ofthe winding leg than its other end, annealing the core, removing themandrel, completely cutting through the core in a plane whose area ofintersection with the core is substantially within the lateral confinesof the winding leg, removing said spacing strip whereby after said coreis spread apart at said out to allow insertion of said winding legthrough a coil window the core can be closed again without excessivelystraining the layers of steel strip, and forcing the cut ends of thecore toward each 8 -& other so that adjacent layers of steel strip areradially separated in order to prevent short circuits between adjacentlayers by burrs raised during the cutting.

4. The method of making a magnetic core for electromagnetic inductionapparatus which comprises, winding a steel strip and a spacing strip ininterleaved relation on a mandrel so as to provide a wound core having awinding leg and a yoke portion, securely fastening the turns of saidsteel strip together in the yoke portion near one end of the windingleg, annealing the core, removing the mandrel, completely cuttingthrough the core within the portion of the winding leg normally occupiedby a conductive winding and near said one end of the winding leg,

removing said spacing strip whereby after said core is spread apart atsaid out to allow the insertion of said winding leg through a conductivecoil window the core can be closed again without excessively strainingthe layers of steel strip, placing a nonmagnetic spacer between the cutends of the core and forcing the cut ends of the core against oppositesides of said nonmagnetic spacer so that adjacent layers of steel stripare radially spaced in order to prevent short circuits between adjacentlayers by burrs raised during the cutting.

JACOB J. VIENNEAU.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS I Date

